Navigation apparatus for vehicle

Abstract: A vehicle navigation apparatus comprises route computing means (1c) for computing an optimum travel route between a departure point and a destination of a vehicle, similarity value calculating means for calculating similarity values each indicating degree of similarity between the pattern of the travel locus of the vehicle and the pattern of each of the travel roads included in a road map, and road selecting means (1b) for selecting, from the road map, candidate travel roads each having a road pattern having a similarity value exceeding a predetermined similarity level. The candidate travel roads includes a present travel road on which the vehicle is currently traveling. The vehicle navigation apparatus further comprises determining means (1c) for determining as to whether or not one of the candidate travel roads overlaps with the optimum travel route and informing means (5a and 5b) for informing to a vehicle driver that the vehicle comes to travel on the optimum travel route when it comes to be determined that one of the candidate travel roads overlaps with the optimum travel route, and informing to the vehicle driver that the vehicle comes to stray from the optimum travel route when it comes to be determined that no candidate travel road overlaps with the optimum travel route. The vehicle navigation apparatus thus constructed can flexibly determine whether the vehicle strays from the optimum travel route, thereby making it possible to prevent the vehicle driver from being perplexed by wrong information.

Description: FIELD OF THE INVENTION The present invention relates to a navigation apparatus for a vehicle and particularly to a navigation apparatus which is to be mounted on a land vehicle such as an automotive vehicle and designed to certainly provide a vehicle driver with information available for a vehicle travel toward his destination. DESCRIPTION OF THE PRIOR ART There have so far been a wide variety of proposals for readily guiding the vehicle driver to his destination in accordance with the available information during the vehicle travel. Such the available information concerns an optimum travel route between the starting point and the destination of the vehicle as well as the present location of the vehicle. A typical example of the vehicle navigation apparatus which are so constructed as to provide the vehicle driver with the optimum travel route is disclosed in Japanese Patent Laid-open Publication No. 2-277200. The optimum travel route and the present vehicle location are acquired through for example "a map matching method" which is so called among those skilled in the art as disclosed in Japanese Laid-open Publication No. 1-53112. According to the map matching method employed in the conventional vehicle navigation apparatus disclosed in the above Japanese Laid-open Publication, the present vehicle location is specified by way of the steps of computing theoretical errors of estimated vehicle locations detected and calculated by numerous sensors in a statistical method, recording the estimated vehicle locations on the travel roads extending within the range of the theoretical errors, updating the estimated vehicle locations in response to the traveling of the vehicle, and determining a present travel road representative of a travel road having a theoretical error smallest in the theoretical errors of the estimated vehicle location of the vehicle. Another vehicle navigation apparatus is proposed in Japanese Laid-open Publication No. 4-313018 (first part of claim 1) and comprises the step of repeatedly computing the optimum travel route to prevent the vehicle from being navigated far away from the destination of the vehicle in the event that the present vehicle location computed by way of the map matching method is deviated from the optimum travel route to have the vehicle travel on a wrong travel road. The conventional vehicle navigation apparatus, however, tends to occasionally detect a wrong present vehicle location with the map matching method designed for computing the present vehicle location when the vehicle is traveling on one of two travel roads closely similar to, adjoining and extending in parallel relationship to each other. In this instance, the vehicle navigation apparatus not only recomputes the optimum travel route but also informs to the vehicle driver that the vehicle strays from the optimum travel route immediately after the vehicle navigation apparatus detects the mistake in the location detection of the vehicle. This results in the fact that the vehicle driver is liable to be perplexed by wrong information and that computing means for computing the optimum travel route is required to perform the needless recomputation of the optimum travel route. International Patent Application No. WO-A-92 04683 discloses a land vehicle navigation apparatus according to the preamble of Claim 1, having input means for start point and destination point and an optimum travel route computing means. The apparatus of D1 includes optimum travel route computing means for calculating an optimum travel route to constantly check whether the vehicle is on-route or off-route by comparing the position with the calculated route. However the apparatus of D1 exhibits problems similar to those described above, particularly when the vehicle is travelling on two close, similar and parallel roads. On the other hand, there have so far been proposed other prior-art vehicle navigation apparatus of this kind which include those disclosed for example in Japanese Laid-open Publication Nos. 62-102113 and 2-154111. The vehicle navigation apparatus disclosed in Japanese laid-open Publication No. 62-102113 is designed to detect branched points represented by intersections in front of the present vehicle location of the vehicle so as to provide a vehicle driver with information about the intersections and the travel roads (referred to hereinlater simply as "cross-road") crossed and connected with the intersections. A typical example is illustrated in Fig. 4 as indicating the information about the cross-roads by way of a map representing screen having a map information displaying section 100 indicative of a present vehicle location 101, a branched point 102, and road identifying numbers A, B and C. In addition to the map information as described above, the map representing screen 100 is designed to have a road information displaying section 110 indicative of information about the name 111 of the branched points 102 and about the cross-roads with the road identifying numbers A, B and C, the latter of which are exemplified by the cross-road names 112 and additional information 113 about travel roads. Therefore, the map representing screen makes it possible for the vehicle driver to acquire such information as the present vehicle location, the branched points and the cross-roads. The navigation apparatus for a vehicle disclosed in Japanese Laid-open Publication No. 2-154111 is constructed to detect the present vehicle location and the name of the next intersection on the travel road toward the vehicle's destination and to have a map representing screen for providing the vehicle driver with information in regard to the names of the intersections and the cross-roads on which the vehicle driver is required to drive his car. The vehicle navigation apparatus herein disclosed renders it possible for the vehicle driver to catch through the map representing screen the information concerning the names of the intersections and the cross-roads having the vehicle driver required to drive his car thereon to the vehicle's destination. The conventional vehicle navigation apparatus as proposed in the foregoing description encounter such disadvantages that the navigation apparatus appear to be unable to detect an accurate present vehicle location while the vehicle is traveling on such areas as having congested and intricate roads and side roads extending in close and side-by-side relationship with certain highways. In order for the vehicle driver to immediately obtain information about a present vehicle location on which the vehicle is currently traveling in the conventional navigation apparatus as disclosed for example in Japanese Laid-open Publication No. 62-102113, the vehicle driver is requested to search a target road identifying number indicative of a present travel road from the road identifying numbers A, B and C displayed on the road information displaying section 100 of the map representing screen so as to select a target road identifying number from the road identifying numbers A, B and C indicated on the road information displaying section 100 of the map representing screen. Another drawback is encountered in that the travel distance between the present vehicle location 101 of the vehicle and the branched point 102 is required to be computed by multiplying the actual travel distance appearing on the map information displaying section 100 of the map representing screen by the reduction scale of the road map displayed thereon. Especially in the case of the relatively large reduction ratio of the road map and the area relatively congested and intricate in the map representing screen of the display unit, it appears to occasionally be unable to search the present vehicle location 101 on the map representing screen of the display unit. It is extremely difficult for the vehicle driver to determine as to how roads the vehicle is currently traveling on in the road map displayed on the map information displaying section 100 of the map representing screen of the display unit. The above road search and determination are time-consuming for the vehicle driver, thereby resulting in paying attention other than the driving operation and thus endangering the driver on the traffic safety. It is therefore an object of the present invention to prevent the vehicle driver from being perplexed by providing a navigation apparatus designed to be able to flexibly determine as to whether the vehicle strays from the optimum travel route. It is another object of the present invention to exclude unnecessary recomputations of the optimum travel routes by providing a navigation apparatus designed to be able to flexibly determine as to whether the vehicle strays from the optimum travel route. SUMMARY OF THE INVENTION According to the present invention there is provided a navigation apparatus for a vehicle, comprising : road map storing means for storing a road map made up of a plurality of travel roads each having said vehicle travel thereon; setting means for setting the departure point and destination of said vehicle; optimum travel route computing means for computing an optimum travel route between the departure point and destination of said vehicle set by said setting means; vehicle location estimating means for estimating vehicle locations at regular intervals; travel locus acquiring means for acquiring a travel locus derived from points on the road map, said points each corresponding to each estimated vehicle location; informing means for informing the vehicle driver whether said vehicle comes to travel on said optimum travel route or to stray from the optimum travel route; and similarity value calculating means for calculating similarity values, each indicating the degree of similarity between the pattern of said travel locus acquired by said travel locus acquiring means and the pattern of each of said travel roads included in said road map; characterized by further comprising : candidate travel road selecting means for selecting, from said road map, candidate travel roads, each having a road pattern having a similarity value exceeding a predetermined similarity value, said candidate travel roads including a present travel road on which said vehicle is currently travelling; determining means for determining as to whether or not one of the candidate travel roads selected by said candidate travel road selecting means overlaps with said optimum travel route computed by said optimum travel route computing means, said informing means informing the vehicle driver that said vehicle comes to travel on said optimum travel route only when it is determined by said determining means that one of the candidate travel roads overlaps with said optimum travel route, and informing the vehicle driver that said vehicle comes to stray from the optimum travel route only when it is determined by said determining means that no candidate travel road overlaps with said optimum travel route. Further embodiments of the invention are described in the dependent claims. BRIEF DESCRIPTION OF THE DRAWINGS The features and advantages of the vehicle navigation apparatus in accordance with the present invention will be more clearly understood from the following description take in conjunction with the accompanying drawings in which: Fig. 1 shows a block diagram representative of the construction of a vehicle navigation apparatus according to the present invention; Fig. 2 shows a block diagram for schematically explaining functions of a locator partially forming the vehicle navigation apparatus shown in Fig. 1 and calculating a present vehicle location; Fig. 3 shows a flowchart representative of the procedure of determination as to whether registered links forming candidate travel roads partially overlaps with links forming an optimum travel route between the departure point and the destination of the vehicle; and Fig. 4 shows a plan view of a conventional display unit having a map representing screen having a map information displaying section indicative of a present vehicle location, a branched point, and road identifying numbers, and a road information displaying section indicative of information about the name of the branched points and the cross-roads with the road identifying numbers. DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to the drawings, first particularly to Fig. 1 thereof, a vehicle navigation apparatus embodying the present invention is shown as comprising a gyro la such as a vibration gyro or an optical fiber gyro for detecting the turning angular velocities of the vehicle at regular intervals, and a terrestrial magnetism sensor 2b for detecting another vehicle travel direction according to the terrestrial magnetism (the magnetic field of the earth) at regular intervals. Based on the output of the gyro la or terrestrial magnetism sensor 2b, variations of the vehicle travel direction are calculated and integrated in order to obtain vehicle locations. Therefore, at least one of the gyro la and the terrestrial magnetism sensor 2b forms vehicle direction variation sensor for detecting the variations of the travel direction of the vehicle at regular intervals. However, the vehicle travel direction obtained from the gyro la is not an absolute direction so that the vehicle travel direction comes to drift, while the travel direction obtained from the terrestrial magnetism sensor 2b tends to include a gross error when the vehicle passes a railroad crossing, an iron or steel bridge, a large vehicle such as a truck or bus or the like. Consequently, from the gyro la and the terrestrial magnetism sensor 2b is selected one direction sensing device depending upon a preferable sensing condition. The vehicle navigation apparatus further comprises a vehicle speed sensor 2a for detecting the travel speed of the vehicle, and a shift sensor 2c for detecting shift positions assumed by a shift control lever of the vehicle to represent such conditions as to have the vehicle moving forward or backward. The vehicle speed sensor 2a is constituted by, for example, a wheel speed sensor for detecting the wheel speed of the vehicle. In this case, the wheel speed detected by the wheel speed sensor is required to be converted to the vehicle speed. The travel distance of the vehicle results from the vehicle speed data and the forward or backward movement data and as a consequence the vehicle speed sensor 2a and the shift sensor 2c collectively form a travel distance sensor for detecting the travel distance of the vehicle at regular intervals. All of the output data derived from the gyro 1a, vehicle speed sensor 2a, the terrestrial magnetism sensor 2b and the shift sensor 2c are available for an estimation of vehicle location. For instance, the vehicle location can be estimated in a manner integrating the travel distances detected by the speed sensor 2a and the shift sensor 2c at the regular intervals and integrating the turning angular velocities detected by the gyro 1a at the regular intervals. On the other hand, the reference character 2d denotes a global positioning system (hereinafter simply referred to as "GPS") designed to receive radio waves from a plurality of artificial satellites revolving around the earth to produce the location data based on the received radio waves. Therefore, the GPS or a sensing unit constituted by the gyro 1a, vehicle speed sensor 2a, the terrestrial magnetism sensor 2b and the shift sensor 2 forms location data producing means for producing location data indicative of the locations of the vehicle. The vehicle navigation apparatus further comprises a CD-ROM (Compact Disk - Read Only Memory) unit 3 and a CD-ROM 3a operably and detachably received in the CD-ROM unit 3. The CD-ROM 3a is a sort of a read-only nonvolatile recording medium having large capacity but, if desired, may be replaced with an IC (Integrated Circuit) memory card, a mini disk, a magnetic tape and so on. The CD-ROM 3a defines now map storing means for storing a road map made up of a plurality of travel roads each having the vehicle travel thereon. More specifically, the CD-ROM 3a stores a road map data representative of a graphically displayed road map specially made so as to have a reduction scale of 1 to 2,500 and divided into a plurality of mesh sections. The road map data comprises two different type data constituted by trunk travel road data indicative of trunk travel roads such as superhighways, automobile roads, highways, state highways, provincial highways, country trunk highways, and all travel road data indicative of all travel roads on the road map inclusive not only of the aforementioned trunk travel road but also of all minor roads such as town roads and village roads. Each of the travel roads defined by the road map data memorized in the CD-ROM 3a is indicated by nodes and links. Each of the nodes is representative of a coordinate specifying the turning point (junction) or corner of the travel road, the node defined by the turning point being permitted to be called a turning-point node, while the node defined by the corner being permitted to be called an interpolation node. In addition, the node is defined by node data indicative of the node number, the address of the node in a mesh section adjoining the mesh section originally including the node in the case that the node is shown in the adjoining mesh sections, and an address of a link extending from the node. Each of the links is, on the other hand, indicative of road segment between the adjoining nodes, and defined by link data indicative of the link number of the link, addresses of starting and ending nodes at the both ends of the link, the distance of the road segment defined by the link, the direction in which the vehicle travels on the road segment defined by the link, the vehicle travel time during the travel on the road segment in the direction, the sort of a travel road partially defined by the link, the width of a travel road partially defined by the link, and information of traffic restrictions including the one-way, right-or left-turn restriction in a road partially defined by the link. The traffic restriction information covers all the trunk roads and partially covers miner roads. The vehicle navigation apparatus further comprises an input switching unit 4 operated by the vehicle driver, a display unit 5a such as an CRT (Cathode Ray Tube) display or a liquid crystal display for displaying information to guide the vehicle driver to a destination, a loudspeaker unit 5b for generating voice for the information, and an AV (Audio and Visual) unit 5 for controlling the display unit 5a and the loudspeaker unit 5b. The input switching unit 4 is constituted by a plurality of switches having the vehicle driver input his various instructions thereto. In response to the instructions by the vehicle driver, for instance, the operation of the vehicle navigation apparatus is started and stopped, and a cursor indicated on a screen of the display unit 5a is moved. The display unit 5a is designed to display the road map in part and to enable the road map to be scrolled in accordance with the instruction inputted by the vehicle driver through the input switching unit 4, so that the vehicle driver obtains a desirable area of the road map on the screen of the display unit 5a. In addition to the road map, the display unit 5a is adapted to display an initial setting menu from the AV unit 5 before the vehicle starts to travel. If the departure point and destination on the displayed road map is touched by the vehicle driver under the condition that the initial menu is displayed on the screen of the display unit 5a, the departure point and destination of the vehicle are inputted to the AV unit 5 through the display unit 5a. Therefore, the AV unit 5 and the display unit 5a collectively defines setting means for setting the departure point and destination of the vehicle. Incidentally, the departure point can be regarded as a present vehicle location detected by the vehicle navigation apparatus. For this reason, the departure point of the vehicle is recognized in general by the AV unit 5 without the departure point input operation of the vehicle driver. The vehicle navigation apparatus further comprises a locator 1b having a function for estimating vehicle locations at regular intervals on the basis of the location data produced by the location data producing means. The vehicle location is estimated by the locator 1b in a manner integrating the travel distances detected by the vehicle speed sensor 2a and the shift sensor 2c and integrating the turning angular velocities detected by the gyro la. The locator 1b further has functions for calculating a vehicle existing area covering the estimated vehicle location and having distribution of vehicle existing probabilities that the vehicle exists on locations included in the vehicle existing area and inclusive of the estimated vehicle location, and for selecting preliminary travel roads from travel roads each partially surrounded by and in the vehicle existing area. The distribution of vehicle existing probabilities is largest at the estimated vehicle location and gradually decreased in a direction away from the estimated vehicle location. The locator 1b further has functions for acquiring a travel locus defined by the estimated vehicle locations, and for calculating similarity values each indicating degree of similarity between the pattern of the acquired travel locus and the pattern of each of the selected preliminary travel roads. The locator 1b further has functions for selecting, from the preliminary travel roads, candidate travel roads each having a road pattern having a similarity value exceeding a predetermined similarity value, the candidate travel roads including a present travel road on which the vehicle is currently traveling, and for specifying on the basis of the estimated vehicle location the present vehicle location on a candidate travel road having a road pattern with the largest similarity value. The locator 1b further has a function for modifying the predetermined similarity level in such a manner that the predetermined similarity level is raised when it comes to be determined that one of the candidate travel roads overlaps with the optimum travel route, and that the predetermined similarity level is lowered when it comes to be determined that no candidate travel road overlaps with the optimum travel route. The determination of the overlapping of the candidate travel road with the optimum travel route is made by a control unit 1c described hereinlater. The control unit 1c partially forms the vehicle navigation apparatus and is constituted by a micro computer, a figure processor and an image processing memory. Additionally, the control unit 1c designed to control the locator 1b, the CD-ROM unit 3 and the input switching unit 4 and the AV unit 5, and have a function for computing an optimum travel route between the departure point and destination of the vehicle set by the display unit 5a and the AV unit 5. The control unit 1c further has functions for determining as to whether or not one of the candidate travel roads selected by the locator 1b overlaps with the computed optimum travel route, and for recomputing the optimum travel route between the present vehicle location and destination of the vehicle only when it comes to be determined that no candidate road overlaps with the optimum travel route. The optimum travel route between the departure point and destination of the vehicle is computed, for instance, by way of a so-called "Dijkstra method" disclosed in Japanese Patent Laid-open Publication No. 1-138409. In the Dijkstra method herein disclosed, a node or link closest to the destination of the vehicle forms a start point, while a node or link closest to the departure point of the vehicle forms an end point. Assuming that a plurality of links successively connected to one another and leading from the start point to the end point forms a tree, link costs of all the links constituting the tree is calculated and then link costs of links forming a travel route from the start point to the end point are successively added to calculate route cost of the travel route. Similarly, route costs of other travel routes from the start point to the end point is calculated. A travel route having the smallest route cost is selected from all of the travel routes leading from the start point and the end point and forms the optimum travel route between the departure point and destination of the vehicle. In advance of evaluating the link cost, a travel distance, travel time, whether superhighways are used or not, number of turns, probability of travel on trunk roads, avoidance of zones where traffic accidents occur frequently, driver's interest and so on are taken into consideration. The control unit 1c is further adapted to read out road map data indicative of a desirable road map area from the CD-ROM 3a through the CD-ROM unit 3 and calculate guidance display data indicative of guidances displayed on the screen of the display unit 5a. In response to instructions from the control unit 1c through the AV unit 5, the display unit 5a is adapted to display on its screen the information that the vehicle comes to travel on the optimum travel route when it comes to be determined by the control unit 1c that one of the candidate travel roads overlaps with the optimum travel route, and that the vehicle comes to stray from the optimum travel route when it comes to be determined by the control unit 1c that no candidate travel road overlaps with the optimum travel route. Similarly, the loudspeaker unit 5b is adapted to voice the information that the vehicle comes to travel on the optimum travel route and that the vehicle comes to stray from the optimum travel route in response to the instructions from the control unit 1c through the AV unit 5. At least one of the display unit 5a and the loudspeaker unit 5b forms therefore informing means for informing to the vehicle driver that the vehicle comes to travel on the optimum travel route when it comes to be determined that one of the candidate travel roads overlaps with the optimum travel route, and informing to the vehicle driver that the vehicle comes to stray from the optimum travel route when it comes to be determined that no candidate travel road overlaps with the optimum travel route. Now, the operations of the locator 1b will be described hereinlater in detail with reference to Fig. 2 which shows a block diagram indicative of functions of the locator 1b in order to make easy the understanding of the operation thereof. The direction data outputted from the gyro 1a and the terrestrial magnetism sensor 2b are fed to an input processing unit 22 to estimate an travel direction of the vehicle by way of appropriate correction and filtering processes. At the same time, the distance data outputted from the speed sensor 2a and the shift sensor 2c are fed to the input processing unit 22 to obtain a travel distance of the vehicle. Based on the estimated travel direction and the travel distance, a vehicle location at the present time is estimated by a present vehicle location estimating unit 23. In addition, the estimated vehicle location is updated by the present vehicle location estimating unit 23 on the basis of vehicle location data indicative of an up-to-date present vehicle location corrected by a location resetting unit 25. Then, a present vehicle travel road on which the vehicle is currently traveling is acquired by the travel road estimating unit 24, the present vehicle travel having the largest similarity value. At the same time, a present vehicle location is specified on the present vehicle travel road by the travel road estimating unit 24, the present vehicle location on the present travel road being closest to the estimate vehicle location. The location resetting unit 25 feeds location data indicative of the specified present vehicle location to the present vehicle location estimating unit 23. If a difference between the vehicle position estimated by the present vehicle location estimating unit 23 and the present vehicle location specified by the travel road estimating unit 24 is comparatively small, the repeated calculations of the present vehicle road and the present vehicle location result in a road coincidence condition indicating that the vehicle location estimated and updated by the present vehicle location estimating unit 23 is coincident with the present vehicle location specified by the travel road estimating unit 24. In other words, the road coincidence condition means that the vehicle location estimated by the present vehicle location estimating unit 23 is an actual present vehicle location If, on the contrary, the difference between the vehicle position estimated by the present vehicle location estimating unit 23 and the present vehicle location specified by the travel road estimating unit 24 is comparatively large, the repeated calculations of the present vehicle road and the present vehicle location result in a road inconsistency condition indicating that the vehicle location estimated and updated by the present vehicle location estimating unit 23 is inconsistent with the present vehicle location specified by the travel road estimating unit 24. In other words, the road inconsistency condition means that the present travel road estimated by the travel road estimating unit 24 is not an actual present travel road. In this case, the location resetting unit 25 cannot correct the estimated vehicle location so that the estimated vehicle location is outputted from a present vehicle location outputting unit 26 as it is, thereby resulting in the fact that the outputted vehicle location obtained only through a so-called "dead-reckoning" is used for guiding the vehicle driver to the destination. The road coincidence condition and the road inconsistent condition are detected by a control judgment unit 21. Incidentally, the links of the selected travel road within the vehicle existing area will be called "registered links" in the following description. The registered links, the link numbers of the registered links and the similarity values of the registered links are memorized by the control judgment unit 21. Based on the link data of the registered links from the control judgment unit 21, the control unit lc determines as to whether or not the registered links partially overlap links of the optimum travel route, i.e., whether or not one of the candidate travel roads overlaps with the optimum travel route by performing a routine shown in Fig. 3. First, determination is made as to whether or not the optimum travel route is computed at step S1. If it is judged at the step 1 that optimum travel route has been computed, control leads to step S2 so as to judge whether or not a link number data indicative of link numbers of the registered links are supplied from the locator 1b. If, at the step S2, it is judged that the link numbers of the registered links has been received from the locator 1b, the link numbers of the registered links are compared with the link numbers of the links forming the optimum travel route at step S3. As hereinbefore described, the similarity values of the registered links is larger than the aforementioned predetermined similarity value. If, for this reason, the predetermined similarity value is extremely small, the significance of the comparison of the link numbers is reduced. If, on the contrary, the predetermined value is extremely large, the number of the registered links expected to be compared is decreased. In the unusual case, registered links forming only one candidate travel road is compared with the links forming the optimum travel route. As a consequence, timing of a determination that the vehicle strays from the optimum travel route is extremely early, thereby making it impossible to resolve the disadvantage of the aforementioned conventional vehicle navigation apparatus. If, at step S4, it is judged that there are registered links having link numbers which are in part equal to the link numbers of the links of the optimum travel route, judgment is made as to whether a travel route flag indicates "0" or "1" at step S5. The travel route flag means that the vehicle is traveling on the optimum travel route when the travel route flag indicates "1", while the travel route flag means that the vehicle strays from the optimum travel route when the travel route flag indicates "0". If it is judged at the step S5 that the travel route flag indicates "0", the control unit 1c at Step S6 produces guide display data indicative of information that the vehicle comes to travel on the optimum travel route in order to transmit the information to the vehicle driver since the vehicle has strayed from the optimum travel road hitherto. If at the step S5 it is judged that the travel route flag indicates "1", the control unit 1c produces no guide display data since the vehicle has traveled on the optimum travel route hitherto, and then the control leads to step S7 so as to set the travel route flag to "1". If, in the meantime, it is at the step S4 judged that there is no registered link having link number partially equal to the link numbers of the links of the optimum travel route, determination is made as to whether or not the travel route flag indicates "0" at step S8. If it is determined that the travel route flag indicates "1", the control unit 1c at Step S9 produces guide display data indicative of information that the vehicle comes to stray from the optimum travel route in order to transmit the information to the vehicle driver since the vehicle has traveled on the optimum travel road hitherto, and then the travel route flag is set to "0" at step S10. If at the step it is determined that the travel route flag indicates "0", the control returns the step S1. As will be understood from the aforesaid description, the control unit 1c determines as whether or not one of the candidate travel roads having similarity values each exceeding the predetermined similarity value overlaps with the optimum travel route. When one of the candidate travel roads comes to overlap with the optimum travel route, the information that the vehicle comes to travel on the optimum travel route is transmitted to the vehicle driver through the display unit 5a or the loudspeaker unit 5b. When, on the contrary, no candidate travel road comes to partially overlap with the optimum travel route, the information that the vehicle comes to stray from the optimum travel route is transmitted to vehicle driver through the display unit 5a or the loudspeaker unit 5b. The plural candidate travel roads are compared with the optimum travel road in a usual way. In this case, the determination of the overlapping of the candidate travel road with the optimum travel route is more flexible than that in a case which only one candidate travel road is compared with the optimum travel road. More specifically, assuming that the vehicle is traveling on one of two travel roads adjoining and extending in parallel relationship to each other, degree of similarity between one of the travel roads and the travel locus resulting from the estimated vehicle locations is approximate to that between the other of the travel roads and the travel locus. If only one candidate travel road is required to be selected, a candidate travel road on which the vehicle is not currently traveling is apt to be selected. In this instance, the selected candidate travel road does not overlap with the optimum travel route. However, it is certain that the vehicle is traveling on the optimum travel route toward the destination in any case and as a consequence it is unnecessary for the vehicle driver to obtain information that the vehicle strays from the optimum travel route. In the vehicle navigation apparatus of the present embodiment, both the candidate travel roads adjoining and extending in parallel relationship to each other are selected so that no information is transmitted to the vehicle driver so far as no candidate travel road comes to overlap with the optimum travel road as will be understood from the aforesaid explanation. Consequently, the vehicle driver can be prevented from being perplexed by the wrong information. It is thus informed to the vehicle driver that the vehicle comes to stray from the optimum travel route when no candidate travel road comes to overlap with the optimum travel road. If however desired, the optimum travel route may be recomputed by the control unit 1c in addition to or in place of the information transmitting operation only when it comes to be determined that no candidate travel road comes to overlap with the optimum travel road. In this case, the optimum travel route can be prevented from being frequently recomputed by the control unit 1c, thereby enabling the control unit 1c to effectively carry out other calculations. Additionally, the predetermined similarity level which is a criterion for the selection of the candidate travel road may be modified by the control unit 1c in such a manner that the predetermined similarity level is raised when it comes to be determined that one of the candidate travel roads partially overlaps with the optimum travel route, and that the predetermined similarity level is lowered when it comes to be determined that no candidate travel road partially overlaps with the optimum travel road. In this event, once it is determined that the vehicle comes to travel on the optimum travel route, wrong determination is frequently not made as to whether the vehicle strays from the optimum travel route. As a result, the vehicle driver rarely obtains wrong information based on the wrong determination, thereby making it possible to prevent the vehicle driver from being perplexed by the wrong information for a long time.

Claims: A navigation apparatus for a vehicle, comprising : road map storing means (3a) for storing a road map made up of a plurality of travel roads each having said vehicle travel thereon; setting means (5, 5a) for setting the departure point and destination of said vehicle; optimum travel route computing means (1c) for computing an optimum travel route between the departure point and destination of said vehicle set by said setting means (5, 5a); vehicle location estimating means (1a, 1b, 2a, 2b, 2c, 2d) for estimating vehicle locations at regular intervals; travel locus acquiring means (1b) for acquiring a travel locus derived from points on the road map, said points each corresponding to each estimated vehicle location; informing means (5a, 5b) for informing the vehicle driver whether said vehicle comes to travel on said optimum travel route or to stray from the optimum travel route; and similarity value calculating means (1b) for calculating similarity values, each indicating the degree of similarity between the pattern of said travel locus acquired by said travel locus acquiring means (1b) and the pattern of each of said travel roads included in said road map; characterized by further comprising : candidate travel road selecting means (1b) for selecting, from said road map, candidate travel roads, each having a road pattern having a similarity value exceeding a predetermined similarity value, said candidate travel roads including a present travel road on which said vehicle is currently travelling; determining means (1c) for determining as to whether or not one of the candidate travel roads selected by said candidate travel road selecting means (1b) overlaps with said optimum travel route computed by said optimum travel route computing means (1c), said informing means (5a, 5b) informing the vehicle driver that said vehicle comes to travel on said optimum travel route only when it is determined by said determining means (1c) that one of the candidate travel roads overlaps with said optimum travel route, and informing the vehicle driver that said vehicle comes to stray from the optimum travel route only when it is determined by said determining means (1c) that no candidate travel road overlaps with said optimum travel route. A navigation apparatus for a vehicle as set forth in claim 1, further comprising road specifying means (1b) for specifying on the basis of said estimated vehicle location a present vehicle location on a candidate travel road having a road pattern with the largest similarity value. A navigation apparatus for a vehicle as set forth in claim 2, wherein said optimum travel route computing means (1c) recomputes the optimum travel route between the present vehicle location and the destination of said vehicle only when it is determined by said determining means (lc) that no candidate travel road overlaps with said optimum travel route. A navigation apparatus for a vehicle as set forth in claim 1, in which said setting means comprises an input unit (5, 5a) having the vehicle driver input thereto for selecting the destination of said vehicle. A navigation apparatus for a vehicle as set forth in claim 1, further comprising similarity level modifying means (1c) for modifying said predetermined similarity level in such a manner that said predetermined similarity level is raised when it is determined by said determining means (1c) that one of the candidate travel roads overlaps with said optimum travel route, and that said predetermined similarity level is lowered when it is determined by said determining means (1c) that no candidate travel road overlaps with said optimum travel route. A navigation apparatus for a vehicle as set forth in claim 1, in which said vehicle location estimating means comprises: a distance sensor (2a, 2c) for detecting the travel distances of said vehicle at regular intervals; and a travel direction variation sensor (1a, 2c) for detecting variations in the travel direction of said vehicle at regular intervals; the vehicle location being estimated by said vehicle location estimating means by integrating the travel distances detected by said distance sensor (2a, 2c) and by integrating the variations in the travel direction detected by said travel direction variation sensor (1a, 2c). A navigation apparatus for a vehicle as set forth in claim 1, in which said vehicle location estimating means comprises a global positioning system (2d) for receiving radio waves from a plurality of artificial satellites revolving around the earth to produce location data indicative of locations of the vehicle based on the received radio waves. A navigation apparatus for a vehicle as set forth in claim 1, in which said informing means comprises a display unit (5a) for displaying on its screen the information that said vehicle comes to travel on said optimum travel route and that said vehicle comes to stray from the optimum travel route. A navigation apparatus for a vehicle as set forth in claim 1, in which said informing means comprises a loudspeaker unit (5b) for voicing the information that said vehicle comes to travel on said optimum travel route and that said vehicle comes to stray from the optimum travel route. A navigation apparatus for a vehicle as set forth in claim 1, further comprising: vehicle existing area calculating means (1b) for calculating a vehicle existing area covering said estimated vehicle location and having a distribution of vehicle existing probabilities that said vehicle exists on locations included in said vehicle existing area and inclusive of said estimated vehicle location, said distribution of vehicle existing probabilities being largest at the estimated vehicle location and gradually decreasing in a direction away from the estimated vehicle location; and preliminary road travel selecting means (1b) for selecting preliminary travel roads from travel roads each partially surrounded by and in said vehicle existing area calculated by said vehicle existing area calculating means (1b); wherein said candidate travel roads are selected by said candidate travel road selecting means (1b) from said preliminary travel roads selected by said preliminary travel road selecting means (1b).

Inventors: ODAGAKI HIDEO, TSUDA SHINGO, ODAGAKI, HIDEO, TSUDA, SHINGO, ODAGAKI, HIDEO, C/O OSAKA WORKS OF, TSUDA, SHINGO, C/O OSAKA WORKS OF
Applicants: SUMITOMO ELECTRIC INDUSTRIES, SUMITOMO ELECTRIC INDUSTRIES, LIMITED
Application year: 1994
Main classification: G01C21
IPC codes: G01C21